1. Field of the Invention
The present invention relates to optical based input touch display devices, and more particularly, to shadow detection for optical based input touch devices using linear splitting of optical beams and grey-scale calculations for detecting the shadow edge and center of an input device.
2. Background of the Invention
User input devices for data processing systems can take many forms. Two types of relevance are touch screens and pen-based screens. With either a touch screen or a pen-based screen, a user may input data by touching the display screen with an input device, such as a stylus, pen or finger.
One conventional approach to providing a touch or pen/stylus-based input system is to overlay a resistive or capacitive film over the display screen. This approach has a number of problems. Foremost, the film causes the display to appear dim and obscures viewing of the underlying display. To compensate, the intensity of the display screen is often increased. However, in the case of most portable devices, such as cell phones, personal digital assistants and laptop computers, the added intensity requires additional power, reducing the life of the battery of the device. The films are also easily damaged. In addition, the cost of the film scales dramatically with the size of the screen. With large screens, the cost is therefore typically prohibitive.
Another approach to providing touch or pen/stylus-based input systems is to use an array of source Light Emitting Diodes (LEDs) along two adjacent X-Y sides of an input display and a reciprocal array of corresponding photodiodes along the opposite two adjacent X-Y sides of the input display. Each LED generates a light beam directed to the reciprocal photodiode. When the user touches the display, with either an input device, the interruption in light beams are detected by the corresponding X and Y photodiodes on the opposite side of the display. The data input is thus determined by calculating the coordinates of the interruptions as detected by the X and Y photodiodes. This type of data input display, however, also has a number of problems. A large number of LEDs and photodiodes are required for a typical data input display. The position of the LEDs and the reciprocal photodiodes also need to be aligned. The relatively large number of LEDs and photodiodes, and the need for precise alignment, make such displays complex, expensive, and difficult to manufacture.
Yet another approach involves the use of polymer waveguides to both generate and receive beams of light from a single light source to a single array detector. With known polymer waveguides, an array of light transmitting lenses, each coupled to the light source through a waveguide, is positioned on one side of touch input display. An opposing array of receive lenses are positioned on the opposite side of the display. Each of the receive lenses have a corresponding waveguide that is optically coupled to a light detector such as a photodiode. During operation, light from the light source is transmitted through the waveguide and the transmit lenses, creating a plurality of collimated light beams adjacent the surface of the display. On the opposing side of the display, the lenses receive the collimated light, which is conveyed to the light detectors through the waveguides. When a data entry is made, using an input device contacting the display, the collimated light at the point of contact is interrupted. The light detectors determine the location of the interrupt, and based on the location, determine the data entry. For more information on polymer waveguides, see for example U.S. patent application Ser. No. 11/498,356, US patent publications 2005/0271319, 2006/0001653, 2006/0002655, 2006/0001654, 2005/0271326, 2005/0271983, 2005/0201681 and U.S. Pat. No. 7,099,553, all incorporated herein by reference for all purposes.
A number of issues are associated with the aforementioned touch screens using polymer waveguides. Foremost, each transmit and receive channel requires a dedicated waveguide. Since a significant number of transmit and receive channels are needed to obtain the necessary input resolution, a large number of waveguides are required. Touch screens are often used with small to medium sized consumer items, such as cell phones and PDAs. The optical touch sensor therefore typically needs to fit into a small space, ideally integrated into the display. Since the waveguide structures are usually planar, the number of waveguides used, and hence the system resolution, can be limited by the area available for the waveguide structures.
An optical based input touch display device with high resolution shadow detection using the linear splitting of waveguides among transmit and receive lenses and grey-scale calculations for shadow edge and center detection is therefore needed in order to minimize the space occupied by the waveguide structures.